Program / Course 14: Arguments for the Existence of God / Lesson 3.1
What you will learn
- State the argument from motion, the argument from causes and the argument from contingency.
- Explain what Aquinas means by motion and by an essentially ordered series.
- Identify the premise in each way that an objector is most likely to deny.
- Describe what each way concludes and what it leaves open.
The big idea
Thomas Aquinas, in the Summa Theologiae (first part, question 2, article 3), gives five short arguments for God, called the Five Ways. The first three are cosmological: they begin from something observed in the world, namely change, causation and contingency, and argue that each points to something that does not itself depend on anything else. Aquinas writes in a compressed style, and the arguments are easily misread as being about the first event in time. They are mainly about what sustains things now.
Key terms
- Motion (Latin, motus)
- For Aquinas, any change, including a thing coming to be what it was not, not only movement in space.
- Act and potency
- Aristotle’s pair of terms. A thing in potency can become something; a thing in act already is something. Change is the reduction of potency to act.
- Efficient cause
- The thing that brings about an effect, as a builder is the efficient cause of a house.
- Essentially ordered series
- A series of causes in which each member depends on the one above it now, as a hand moves a stick that moves a stone.
- Accidentally ordered series
- A series in which each member produced the next but does not need it to keep acting, as a father begets a son who begets a grandson.
- Contingent being
- A thing that can exist or not exist, as shown by the fact that things come to be and pass away.
- Summa Theologiae
- Aquinas’s great unfinished work of theology, written between 1265 and 1274.
Background
Aquinas (1225 to 1274) was a Dominican friar and teacher in Paris and Italy. The Five Ways are a brief passage in the Summa, taking up less than two pages. Aquinas does not treat them as the center of his thought. They answer the question whether God exists, which he asks mainly to clear the ground for his long study of what God is.
He draws on Aristotle, on the Muslim philosophers Avicenna and Averroes, and on the Jewish philosopher Maimonides. Aquinas notes the objection that God’s existence is evident and needs no proof, and replies that it is not evident to humans, so it must be shown from effects. This is how he begins each way.
The first three ways are often grouped as cosmological because they argue from features of the world to a cause. The remaining two are treated in Module 5.
Step-by-step explanation
Step 1: The first way, from motion
Aquinas observes that some things in the world are in motion, meaning that they are changing. Whatever is changed is changed by another, because a thing cannot give itself what it does not have. Water cannot make itself hot, but fire can. If that other thing is also being changed, it needs another. But this cannot go on forever, because then there would be no first mover and so no other mover, just as a stick moves nothing unless a hand moves it. So there must be a first mover that is not itself moved by anything else. This, says Aquinas, everyone understands to be God.
A key point is the kind of series. The causes are acting at the same time. The hand moves the stick now. It is not about a first moment of history.
Step 2: The second way, from efficient causes
Aquinas notes that there is an order of efficient causes in the world. Nothing is the efficient cause of itself, because it would then be prior to itself. In a series of efficient causes, the first is the cause of the middle, and the middle of the last. If the first is removed, the rest are removed. So a series cannot go to infinity, and there must be a first efficient cause, which all call God.
Step 3: The third way, from possibility and necessity
Things come into being and pass away, which shows that they are possible to be and not to be. Aquinas argues that if everything were such a thing, then at some time nothing would have existed, and then nothing would exist now, since nothing comes from nothing. So there must be something necessary. Its necessity either comes from another or from itself. A series of necessary things deriving their necessity from others cannot go to infinity, so there must be a being that is necessary through itself and is the cause of necessity in others.
Many philosophers think this step contains an error, the claim that if everything were contingent then at some time nothing would have existed. This is discussed under the objections.
Step 4: The common pattern
Each way has three parts: an observed feature of the world, a claim that the explanation cannot go back without end, and a conclusion that something exists that is not itself in the dependent condition. A student should state each way in these three parts and identify which claim is the key one.
Step 5: Read the ways correctly
Three cautions. First, Aquinas elsewhere said that the beginning of the world cannot be proved by reason, so these ways are not about a first moment. Second, the conclusion at the end of each way is a bare statement. Aquinas follows them with questions on God’s simplicity, goodness and unity. Third, the ways are not neutral: they come inside a work of theology written for students already inside the faith.
- What does Aquinas mean by motion, and how is that wider than movement through space?
- Why does he think a series of simultaneous movers cannot go on forever?
- Is the third way an argument from time, or from dependence?
- Which of the three ways seems strongest to you, and why?
- Where might an objector push back in the first way?
- How does the order of efficient causes differ from a family tree?
Examples
The hand, the stick and the stone
Aquinas’s own image is a stick moving a stone and a hand moving the stick. Take away the hand and the stick does nothing. The example shows what he means by a series in which each member depends on the one above it now.
Father and son
A man begets a son, who begets a grandson. The grandfather may be dead while the grandson lives. This is an accidentally ordered series, in which earlier members are not needed for later ones to act. Aquinas says that an infinite series of this kind is not what the argument excludes.
A light and its source
A lamp shines in a room only while it is connected to power. Cut the connection and the light stops. This modern picture helps illustrate dependence at present, which is what the first two ways concern.
Different perspectives
Catholic
The Catholic Church holds Aquinas in the highest regard, and the First Vatican Council taught that God can be known from created things by natural reason. Thomists defend the ways as sound and not about time. The Church has not defined the Five Ways as the required proofs.
Orthodox
Orthodox theologians usually appreciate that Aquinas saw the limits of what can be said of God, but they are cautious about arguments that treat God as the first member of a series of causes. They stress that God is not a being among beings. Some, such as David Bentley Hart, defend a version of the argument as pointing to the ground of being.
Protestant
Protestant opinion varies. Reformed philosophers like Plantinga hold that belief in God does not need these arguments. Some Lutheran and Reformed theologians treat them with suspicion. Others, including many evangelical philosophers, use cosmological arguments.
Scholarly views
Scholars debate whether Aquinas intended each way as a complete proof or as a sketch, and how to understand the key premises about essentially ordered series. The first way has been read in widely different ways. Careful study of Aristotle’s physics is needed to understand it.
Skeptical views
Skeptics say that modern physics has made the notion of motion as potency into act obsolete, that the argument from an essentially ordered series assumes more than it proves, and that even if a first cause exists, nothing shows it to be God.
Why it matters
The Five Ways are the best-known arguments for God in the Western tradition, and they are widely misrepresented, by defenders and critics alike. Reading them slowly shows how much of the common caricature, such as the idea that they are about a first moment, does not match the text.
Common misunderstandings
Misunderstanding: Aquinas argued that God started the universe long ago.
Correction: The ways concern present dependence. Aquinas held that reason cannot establish that the world had a beginning in time.
Misunderstanding: Each way ends with the full God of the Bible.
Correction: Each ends with a statement that this is what all call God. The fuller account comes in later sections and relies partly on revelation.
Misunderstanding: Aquinas thought faith depends on these proofs.
Correction: He held that they are preambles to faith. Faith itself is a gift and not a conclusion of argument.
Misunderstanding: Modern science has simply refuted the arguments.
Correction: Some of Aquinas’s physical examples are outdated, but defenders argue the metaphysical structure does not depend on them. Critics disagree, and the matter is debated.
Knowledge check
Summarize the first way in a few sentences.
Some things are changing. Whatever changes is changed by another, because nothing gives itself what it lacks. If that other is also changing, it needs another. A chain of simultaneous movers cannot go back without end, since without a first mover none would move. So there is a first mover not moved by anything, which is called God.
What is the difference between an essentially and an accidentally ordered series?
In an essentially ordered series, each member acts only because the one above it is acting now, like a hand moving a stick. In an accidentally ordered series, each member produced the next but does not need it to keep acting, like a father and son. Aquinas’s ways need the first kind to be finite.
What does the third way claim, and what is the objection to its middle step?
It claims that if everything were contingent, at some time nothing would have existed, so something necessary must exist. Critics say that does not follow: each thing could exist at different times without any time at which nothing existed. This is sometimes called the quantifier shift objection.
Why are the ways not arguments for a first moment in time?
Aquinas held that the beginning of the world is known by faith and cannot be proved by reason. The ways are about what keeps things in being and in action now. A world without a beginning, in his view, would still need a first cause in this sense of dependence.
Think it through
- What in your experience seems to depend on something else right now?
- Do you find the distinction between the two kinds of series convincing?
- Does it matter to you if the conclusion is smaller than the biblical God?
- What question would you ask Aquinas if you could?
Independent assignment
The three ways in your own words
In your own notebook, write 350 to 500 words. Read the article on the Five Ways and write the first three ways as numbered steps. For each way, mark the premise an objector is most likely to deny and give one sentence of reason. Then say which way you find hardest to accept and why. Do not send this to anyone.
Further study
- Thomas Aquinas, Summa Theologiae I, Q. 2: The Existence of God Read the whole article and identify the premise an objector will deny in each way.
- Thomas Aquinas, Summa Theologiae Read the first part, questions 2 and 3, for the setting of the ways.
- Stanford Encyclopedia of Philosophy, Thomas Aquinas Read for the background to the Five Ways.
- Stanford Encyclopedia of Philosophy, Cosmological Argument Read the section on Aquinas and the distinction between kinds of series.
- Acts 17 Paul says God gives to all life and breath.
- Colossians 1 Verse 17 says that in Christ all things hold together.